A polyurethane product such as a polyurethane foam, a polyurethane elastomer, elastic fibers, an adhesive or a sealant, and a polyether polyol as a material of e.g. a functional lubricant are produced usually by polymerizing an alkylene oxide such as ethylene oxide or propylene oxide using an initiator having active hydrogen. As a polymerization catalyst for an alkylene oxide, a double metal cyanide complex (hereinafter sometimes referred to as DMC) catalyst has been know. The DMC catalyst is a catalyst containing an organic ligand and a metal salt, and its typical example is a compound having an organic ligand, water and zinc chloride coordinated to zinc hexacyanocobaltate (Zn3[Co(CN)6]2).
The following Patent Document 1 discloses that by using a highly active DMC catalyst employing an organic ligand such as tert-butyl alcohol, the amount of use of the catalyst can be reduced, and a step of removing the DMC catalyst after production of a polyether polyol is unnecessary.
In Example 8 to prepare a polyether polyol, a method is disclosed in which an initiator and a DMC catalyst are put in a reactor and heated at 105° C. to carry out stripping, then the reaction temperature is increased to 145° C., part of propylene oxide is supplied to the reactor in initial vacuum, and while the reactor pressure is carefully monitored, the remaining propylene oxide is gradually added and reacted after the reactor pressure is suddenly decreased, and the system is maintained at 145° C. until the pressure becomes constant.
Further, the following Patent Document 2 discloses a process for producing a polyester ether polyol or a polyester ether monool using a DMC catalyst.
In Example 1 to prepare a polyester ether polyol, a process is disclosed in which an initiator and a DMC catalyst are put in a reactor, the interior in the reactor is replaced with nitrogen, and temperature is increased to 140° C., part of propylene oxide is supplied to the reactor, and after a decrease of the pressure in the reactor and activation of the catalyst are confirmed, the remaining propylene oxide and ε-caprolactone are added, to conduct polymerization reaction while the internal temperature of the reaction is maintained at 140° C.
The following Patent Document 3 discloses, as a process suitable for production of a short chain polyether alcohol exceeding 200 mgKOH/g using a DMC catalyst, a process of preliminarily dispersing the DMC catalyst in an initiator comprising a polyether polyol at a temperature of from 0 to 80° C. to condition the catalyst, then increasing the temperature to the polymerization temperature, and supplying part of an alkylene oxide to activate the catalyst.